U.S. patent number 4,925,303 [Application Number 07/290,749] was granted by the patent office on 1990-05-15 for aircraft piloting aid laser landing system.
Invention is credited to Pavo Pusic.
United States Patent |
4,925,303 |
Pusic |
May 15, 1990 |
Aircraft piloting aid laser landing system
Abstract
A piloting aid system for landing an aircraft in either normal
or adverse weather conditions is disclosed. The system applies a
laser scanning process for determining and correcting the
aircraft's position with respect to the commanded landing
trajectory and for determining the aircraft's speed, altitude, and
distance from the runway. The system provides the possibility to
direct the aircraft exactly towards the runway longitudinal axis
and to level the aircraft exactly parallel to the runway plane all
along the landing trajectory and, consequently, to effect a safe
landing under visibility conditions which would otherwise prevent
landing.
Inventors: |
Pusic; Pavo (Dubrovnik,
YU) |
Family
ID: |
23117389 |
Appl.
No.: |
07/290,749 |
Filed: |
December 27, 1988 |
Current U.S.
Class: |
356/139.03;
340/952; 342/33; 356/141.1; 356/152.3; 73/178T |
Current CPC
Class: |
G01C
9/005 (20130101); G01S 17/50 (20130101); G01S
17/875 (20130101); G05D 1/0676 (20130101) |
Current International
Class: |
G01C
9/00 (20060101); G01S 17/87 (20060101); G01S
17/50 (20060101); G01S 17/00 (20060101); G01C
021/00 () |
Field of
Search: |
;356/141,152 ;73/178T
;340/952,953 ;342/33 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Jordan; Charles T.3
Assistant Examiner: Wendtland; Richard W.
Claims
What is claimed is:
1. A method of determining an aircraft's actual position, speed,
altitude, and distance from the landing runway said aircraft is
approaching, comprising the steps of:
emitting laser beams from at least two laser transmitting means
located in proximity of each wing tip of said aircraft;
reflecting a portion of said laser beams backwards to said aircraft
in accordance with a predetermined pattern;
receiving said reflected laser beams by at least two on board laser
receiving means;
processing data about said emitted laser beams and said reflected
laser beams and transmitting said data to an avionic system for
monitoring and correcting said aircraft's position, and detecting
an accidental error of any of the other on board avionic system's
means.
2. A piloting aid system for aiding in landing of an aircraft on
the landing runway said aircraft is approaching, said system
comprising:
at least two transmitting-receiving apparatuses located in
proximity of each wing tip of said aircraft for emitting laser
beams and receiving reflected returns of said laser beams;
on board computer means coupled to said transmitting-receiving
apparatuses for controlling the process of said apparatuses,
processing data obtained from said apparatuses, and transmitting
said data to an avionic system;
laser beams' reflecting means located along both sides of said
landing runway for reflecting said laser beams in accordance with a
predetermined pattern, said reflecting means positioned parallel to
a longitudinal axis of said runway and being equidistant with
respect to said runway's longitudinal axis.
3. The system according to claim 2, wherein said
transmitting-receiving apparatuses further comprise:
transmitting means for emitting said laser beams and transmitting
data about said emitting to said computer means;
receiving means coupled to said transmitting means for receiving
said reflected returns and transmitting data about said reflected
returns to said computer means.
4. The system according to claim 2, wherein said computer means
further comprises:
processing means coupled to said transmitting means and to said
receiving means for processing said data obtained from said
transmitting means and said receiving means, for determining actual
position of said aircraft with respect to said landing runway, and
for determining said aircraft's actual speed, altitude, and
distance from said landing runway;
transmitting means coupled to said processing means for
transmitting said data about said aircraft's actual position,
speed, altitude, and distance from said runway to said avionic
system.
5. The system according to claim 2, wherein said reflecting means
include reflective and non-reflective sections for either
reflecting or absorbing (deflecting) said laser beams in accordance
with said predetermined pattern.
Description
BACKGROUND OF THE INVENTION
The present invention relates to the navigation of an aircraft and
in particular to a means for determining the position of an
aircraft with respect to a runway.
Upon aircraft landing, adverse weather conditions such as heavy fog
or rain, causing low visibility, can result in particularly
hazardous conditions. Therefore, despite a sophisticated digital
avionic system installed on the present generation of aircrafts
which defines aircraft's altitude, speed, and distance from a
runway with great precision, there are defined minimum weather
conditions required before an aircraft can continue an approach to
a landing. These weather conditions take into account the
capabilities of the aircraft and the pilot, and the equipment
installed at the airport and require minimum ceiling and minimum
runway visibility because of possibility for an incident to occur.
While making an instrumental approach, an incident may occur
because of even small error, either of equipment installed at an
airport or of an onboard avionic system. A missed approach, which
results either in a go-around procedure and another attempt to land
or a flight to an alternate airport, causes huge expenses to
airline company and great inconvenience for passengers.
The well-known Instrument Landing System (ILS) and Microwave
Landing System (MLS), together with other related means such as
Distance Measuring Equipment (DME), provide the pilot and/or
digital avionic system with accurate information for an approach
and landing. These instruments provide a technique for reaching an
end-of-descent point with great precision. Ideally, once cleared
for descent, an aircraft is left alone to perform the descent from
a top-of-descent point along descent path to an end-of-descent
point where a final flare-out occurs.
A flare-out or flare, which is that portion of the landing
trajectory between the fixed angle glide slope and the touchdown
point on a runway, is the critical portion of the aircraft landing
trajectory during which a pilot must decide either to continue the
landing procedure or to abort the landing and effect the go-around.
Since the systems disclosed in the prior art may not provide the
pilot with a completely accurate position of the aircraft with
respect to the runway longitudinal axis and plane due to the
susceptibilities of the systems, visual contact is necessary to
perform a completely safe landing. The visual contact with the
runway must be possible before the point where the pilot can still
effect a completely safe go-around procedure and, therefore,
conditions where low visibility occurs, mostly due to heavy fog,
prevent landing on airports sometimes for substantial periods of
time.
Therefore, it is an object of the present invention to provide an
inexpensive system which will enable the pilot to determine the
position of the aircraft with respect to the runway with greater
precision than when using only systems know in the prior art. It is
an assumption that the present invention does not eliminate
presently used systems and acts accordingly with any of them by
supplying the digital avionic system with more accurate additional
information regarding the aircraft position with respect to the
runway.
The present invention enables the pilot to position the aircraft
exactly towards the runway longitudinal axis and plane and effect a
safe landing, even in almost zero-zero visibility conditions.
Acting accordingly with existing systems, the present invention can
be used as a reliable and independent secondary means of detecting
an accidental error which may occur due to susceptibility of ILS'
or MLS' means.
SUMMARY OF THE INVENTION
It has been proven that a laser beam can penetrate clouds, fog or
rain for certain distances without losing its extremely high
coherence and provide a nearly ideal straight line which approaches
theoretical limits. In accordance with the present invention, it is
assumed that the possibility for the laser beam to be blocked by
fog, rain or snow can be ignored due to relatively short distance
wherein the laser beam is to be applied for this purpose and
considering that heavy fog (which in most cases causes low
visibility and prevents landing) almost never occurs together with
rain or snow. A narrowness of the laser beam permits sharp
definition of targets and, therefore, lasers can serve as fast,
high-resolution devices for determining the aircraft's position,
speed, distance from the runway, and altitude.
In accordance with the present invention, two laser beams emitted
from two different positions on an aircraft are used to scan
reflective and non-reflective areas located on both sides of the
runway. According to returns received from the reflective areas
along both sides of the runway, highly accurate position, speed,
distance from the runway, and altitude can be calculated. With the
assumption that the reflective and non-reflective areas on both
sides of the runway represent exactly the same values, divergence
from course (runway longitudinal axis and plane) can be derived
from different returns. Also, due to the characteristic of the
laser beam, the aircraft's speed, distance from the runway, and
altitude can be calculated.
In accordance with the present invention, the aircraft starts
emitting laser beams at the defined point on its descending path
and continues this procedure without interruption to the final
touch-down. Returns from the reflective areas are continueously
compared by the onboard computer which indicates to the pilot
and/or digital avionic system any divergence from the commanded
descending and flare path. Information captured by such laser
scanning procedure enables extremely accurate positioning of the
aircraft with respect to the runway longitudinal axis and plane
and, therefore, will enable safe landing even in adverse weather
conditions which do not satisfy current requirements for minimum
ceiling and runway visual range.
The present invention can also be used to provide a pilot of an
aircraft landing on an aircraft carrier with more accurate
information about speed, distance from runway, altitude, and
position with respect to the aircraft carrier runway longitudinal
axis and plane.
All features and advantages of the present invention will become
apparent from the following brief description of drawings and
description of the preferred embodiment.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is the graph showing the aircraft's landing trajectory for
landing on a standard runway.
FIG. 2 is the graph showing the aircraft's landing trajectory for
landing on an aircraft carrier runway.
FIG. 3 is the graph showing the front view of the approaching
aircraft.
FIG. 4 is the graph showing the front view of the approaching
aircraft in the case where the reflected returns are captured by
the receiver located on the opposite wing with respect to the laser
beam transmitter.
FIG. 5 is the block diagram of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, there is shown the part of the aircraft
landing trajectory comprising the final section of the portion
known as a descending path 2 and the portion known as the flare
path 3, wherein the descending path is defined at the fixed angle
with respect to the runway 4 and the flare path 3 starts at the
flare initiation point and terminates at the touch-down point on
the runway 4. The descending path 2, which starts at a
top-of-descent point (not shown on FIGS.) and goes along a glide
slope signal, terminated at the end-of-descent point which is also
defined as the flare initiation point.
Once cleared for descent, the aircraft performs the descent along
the defined glide slope transmitted either by ILS glide slope
transmitter or MLS elevation transmitter. As known from the prior
art, ILS provides .+-.2.degree. glide slope coverage and
.+-.2.degree. localizer coverage while MLS provides 20.degree.
elevation coverage and .+-.60.degree. azimuth coverage.
In accordance with the present invention, the approaching aircraft
1 is provided with two laser transmitters and two receivers 51,
preferably located in the far ends of the aircraft's wings as shown
on FIG. 3. The runway is provided with the reflective areas 6 which
are preferably located along both sides of the runway 4 as shown on
FIGS. 1 and 3. The reflective 6 and nonreflective areas , arranged
in a chipper set format, are stationary and positioned at different
angles required for the purpose of reflecting laser beams 5, shown
on FIGS. 1 and 3, which are transmitted from the aircraft's
different positions along the descending 2 and the flare path 3. It
is assumed that only the reflective areas 6 have to be built along
the runway sides. The remaining runway surface will serve as
non-reflective areas due to its inability to reflect the laser
beams at the required angle.
According to the requirements, the reflective areas 6 can be
located all along the runway 4 or only along the portion of the
runway 4 from its beginning to the touch-down point. Preferably,
the reflective areas are located from a certain defined point in
front of the runway 4 to the touch-down point, as shown on FIG.
1.
In the case of the aircraft 7 landing on the aircraft carrier 10
the reflective areas can be located vertically on both sides of the
carrier runway, as shown on FIG. 2.
In order to enable different types of aircrafts to use the same
reflective areas 6 on the runway 4, it is assumed that the onboard
laser equipment 51 is located correspondingly on each type of
aircraft. Also, in order to obtain the exact direction of the laser
beams 5, the fact that the technique for construction of the
descent path by flight management computer system is based on the
idle thrust performance of a specific aircraft has to be taken into
consideration. The reflective 6 and non-reflective areas along the
runway 4 sides can have any "1" or "0" order, wherein "1"
represents reflective portion of the surface and "0" represents
nonreflective portion of the surface and wherein each individual
"1" and each individual "0" has the same height (width) value. The
applied order has to have a ratio which provides a digital avionic
system and/or pilot with accurate information, with the assumption
that this system is activated after receiving ILS or MLS guidance
signals where the actual aircraft position does not provide any
reasonable possibility for an accidental error regarding the laser
beam returns.
It is assumed that at this particular moment (beginning of scanning
process) the aircraft 1 heads towards the runway 4 and that actual
position of its laser equipment 51 does not allow the possibility
to make an error regarding the scanning of two sets of the
reflective areas 6 which are located on the opposite sides of the
runway 4. Therefore, there is not possibility to obtain returns
which may provide inaccurate data and mislead the digital avionic
system and/or the pilot.
It is to be understood that the reflective 6 and non-reflective
areas may be located beside the runway 4 sides and that the
aircraft onboard laser equipment. 51 does not have to be
stationary, if proven more efficient for the purpose of the
invention. Regardless of their location, both the onboard
transmitters and receivers 51, and the runway reflective areas 6
have to be positioned in a manner which ensures proper scanning in
accordance to the determined landing trajectory 2 and 3. The same
principle has to be applied in the case of landing on the aircraft
carrier 10 wherein the reflective and non-reflective areas are
preferably vertically positioned for purpose of more efficient
scanning
Ideally, the reflective areas 6 are located along both sides of the
runway 4 equidistantly to the runway longitudinal axis. The
distance between the left and right reflective areas 6 corresponds
to the distance between the onboard transmitters and receivers 51
which are also positioned exactly equidistantly with respect to the
aircraft's longitudinal axis. The reflective areas are also
positioned in accordance to the runway's plane.
While the scanning process described herebelow corresponds to one
wherein helium-neon laser and photodiode are most commonly applied,
it is to be understood that this does not represent a limitation
for the present invention. Any kind of laser can be used according
to the most optimal performance and considering all involved
factors during a landing process under adverse weather
conditions.
In accordance with the present invention, the approaching aircraft
1 starts emitting the laser beams 5 from two laser transmitters 51
at the defined point of its descent path 2, as shown on FIG. 1. The
transmitters 51 are located on both aircraft's wings. The laser
beams 5 are emitted at the defined angle in accordance with the
calculated descent path 2 and configuration of the reflective areas
6. As the aircraft 1 descends, the emitted laser beams 5 move
forward over the reflective 6 and non-reflective areas located in
front and along the runway 4. As the beams 5 move over the
reflective areas 6, they are reflected back to the receivers
according to the height (width) difference of these areas. Any
divergence between two simultaneously reflected returns can be
observed with great precision. The returns will diverge in the case
of any incorrectness in the aircraft's position with respect to the
runway longitudinal axis and plane. The reflected returns are
captured by the receivers and processed by the onboard computer
11.
The information obtained from the reflected returns are compared
with each other and according to their divergence the computer 11
defines the position of the aircraft 1 with respect to the runway
4. If there is no divergence between the two simultaneous returns
the aircraft 1 is correctly positioned. All processed information
are permanently transmitted to Flight Management Computer System
(FMCS) in order to be compared with corresponding data obtained
from other avionic system's means and, if required, to correct the
aircraft 1 position. Simultaneously, by measuring the frequency
between the original 5 and reflected beams (Dopper Effect) the
speed of the aircraft 1 is calculated and since the speed of light
is known, by measuring the time taken for the beam 5 to reach and
return from the reflective areas 6 the distance from runway 4 is
also calculated. In addition, since the beam 5 angle, aircraft 1
speed, and distance from runway are known, the altitude is also
calculated. All these data are also transmitted to FMCS to be
compared with corresponding data obtained from other avionic
system's means, in order to detect possible accidental error and
properly position the aircraft 1.
The process is continued along the entire descent path 2 (as shown
in dotted lines on FIG. 1) enabling the aircraft 1 to descend on
the fixed angle glide slope in an extremely precise position with
respect to the runway longitudinal axis and plane due to the fact
that any divergence between two simultaneous reflected returns is
almost instantly indicated to FMCS. Since the most important
purpose of the invention is to enable safe landing under low
visibility conditions caused by fog or clouds which almost never
occur together with a strong wind, it is assumed that the
possibility that one or both of the aircraft's wings (where laser
equipment 51 is located) vibrates due to strong wind can be
ignored.
After the aircraft 1 leaves the fixed angle glide slope at the
flare initiation point, the above described scanning process is
continued, as shown by the dotted lines on FIG. 1. The laser beams
5 are emitted at the same fixed angle with respect to the
aircraft's body but the reflective areas 6 are positioned at
different angles which correspond to changes of the angle of the
emitted laser beams 5 with respect to the runway 4. This change of
the beam's 5 angle with respect to the runway 4 is caused by the
different horizontal positions of the aircraft's longitudinal axis
during the flare 3. Along the flare portion 3 of the landing
trajectory, reflected returns are captured, processed, and
transmitted to FMCS exactly as previously described for the descent
path portion 2 of the landing trajectory. Correspondingly, during
the flare portion 3 of the landing trajectory the present invention
enables extremely proper positioning of the aircraft with respect
to the runway 4 and eliminates the need for minimum vertical and
horizontal visual range required for safe landing for the systems
known in the prior art.
If the reflective areas 6 and onboard laser equipment 51 are
designed for the purpose of taxiing procedure, the aircraft can be
guided by a scanning procedure all the way to the terminal even
under zero-zero visibility conditions.
If proven more efficient for the purpose of the present invention,
the reflective areas 6 can be located in front and beside the
runway 4, as shown on FIG. 4, having a distance wider than the
aircraft's wingspan. Unlike for the above described process,
wherein the laser beams 5 are reflected to the receiver located on
the same side, in this case the laser beams 5 are reflected to the
opposite wing and the returns 52 are captured by the receiver
located opposite to the transmitter, as shown by the dotted lines
on FIG. 4. Accordingly, the beam 5 from the transmitter on the left
wing produces the return 52 to the receiver on the right wing and
vice versa. The reflective areas 6 have to be positioned in a
manner suitable for said reflecting purposes and the beams 5 have
to be emitted in a manner that prevent their collision when the
aircraft's wings are in horizontal position which corresponds to
the horizontal position of the runway 4 plane.
The scanning process corresponds to the previously described one,
with respect to certain differences which will occur due to the
slightly different angles of the simultaneously emitted beams 5.
These differences will be solved by the process of the onboard
computer 11 which further transmits information to FMCS as
described in the previous process.
In the case of the aircraft 7, FIG. 2, landing on the aircraft
carrier 10, the previously described scanning process is performed
along the landing trajectory 8. The laser beams 9 transmitters and
receivers 51 are also located in both aircraft wings as previously
described and the reflective and non-reflective areas are located
on the carrier 10, preferably in vertical position. Refelcted
returns are captured, processed, and transmitted according to the
prevously described process. As previously stated regarding the
aircraft 1 landing on the runway 4, it is also to be understood
that location, position, and movability of both onboard laser
equipment 5 and the reflective areas on the aircraft carrier do not
represent limitations regarding the application of the present
invention for landing on the aircraft carrier.
It is also to be understood that any configuration can be applied,
if proven more efficient for the purpose of the present invention
including the possibility for reverse location of the laser
equipment 51 and the reflective areas 6 wherein the laser
transmitters and receivers are located on the runway and returns
are obtained from the body of the aircraft.
Under the assumption that the reflective areas 6 are built in the
manner to serve this purpose, the present invention can also be
applied in order to perform a completely safe take-off under
zero-zero visibility conditions. In dependance to the position of
the reflective areas 6, this situation may demand that the laser
transmitters are movable in order to be able to emit the laser
beams 5 towards the reflective areas under the required angle. In
accordance with the present invention, the aircraft is guided by
the scanning procedure while taxiing to the take-off starting point
under zero-zero visibility conditions. During the take-off
procedure the laser equipment scans the reflective areas 6 (in the
manner as previously described) and the aircraft is permanently
positioned exactly towards the runway longitudinal axis which
enables a completely safe take-off procedure.
It will be understood that the present invention has been described
in relation to the particular embodiment, herein chosen for the
purpose of illustration and that the claims are intended to cover
all changes and modifications, apparent to those skilled in the
art, which do not constitute departure from the scope and spirit of
the invention.
* * * * *